Begin converting URL struct into modern C++ class

dpid/dpid_common.h

@@ -9,6 +9,11 @@
  * the next patch
  */
 
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
 #include <dirent.h>
 #include <stddef.h> /* size_t */
 #include <sys/types.h> /* ssize_t */
@@ -51,4 +56,8 @@ void errmsg(char *caller, char *called, int errornum, char *file, int line);
 ssize_t ckd_write(int fd, char *msg, char *file, int line);
 ssize_t ckd_close(int fd, char *file, int line);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif